1. Field of the Invention
The present invention relates to a vibration driven motor for obtaining a driving force by generating an elliptic motion in an elastic member.
2. Related Background Art
FIG. 4 is a view showing a conventional linear vibration driven motor.
In the conventional linear vibration driven motor, a vibration member 102 for applying a vibration is disposed at one end side of a rod-like elastic member 101, and a transformer 103 for controlling a vibration is disposed at the other end side thereof. Vibrators 102a and 103a are respectively coupled to the vibration member 102 and the transformer 103. An AC voltage is applied from an oscillator 102b to the vibrator 102a for applying a vibration to vibrate the rod-like elastic member 101, and this vibration becomes a progressive wave when it propagates through the rod-like elastic member 101. A movable member 104, which is in press contact with the rod-like elastic member 101, is driven by the progressive wave.
The vibration of the rod-like elastic member 101 is transmitted to the vibrator 103a via the transformer 103 for controlling a vibration, and the vibrator 103a converts the vibration energy into electric energy. A load 103b connected to the vibrator 103a consumes the electric energy, thereby absorbing the vibration. The transformer 103 for controlling a vibration suppresses reflection at the end face of the rod-like elastic member, thereby preventing generation of a standing wave in a characteristic mode of the rod-like elastic member 101.
In the linear vibration driven motor shown in FIG. 4, the rod-like elastic member 101 must have a length corresponding to the moving range of the movable member 104, and the entire rod-like elastic member 101 must be vibrated, thus increasing the size of the apparatus. In addition, the transformer 103 for controlling a vibration is required to prevent generation of a standing wave in the characteristic mode.
In order to solve the above-mentioned problems, various self-running vibration driven motors have been proposed. For example, a "hetero-degeneracy longitudinal L1--bending B4 mode plate motor" described in "222 Piezoelectric Linear Motors for Application to Driving a Light Pick-Up Element" in "Lecture Papers of 5th Electromagnetic Force Associated Dynamics Symposium" is known.
FIGS. 5A to 5C are views showing a conventional hetero-degeneracy longitudinal L1--bending B4 mode plate motor, in which FIG. 5A is a front view, FIG. 5B is a side view, and FIG. 5C is a plan view.
An elastic member 1 has a rectangular planar shape, and driving force output portions 1a and 1b as projecting portions are formed on one surface of the member 1. The driving force output portions 1a and 1b are arranged at antinode positions of a bending vibration B4 mode generated in the elastic member 1, and are pressed against an object such as a guide rail 4 (see FIG. 7).
Electro-mechanical converting elements 2a and 2b are elements for converting electric energy into mechanical energy, and are adhered on the other surface of the elastic member 1. The elements 2a and 2b generate a longitudinal vibration L1 mode and a bending vibration B4 mode in the elastic member 1.
The operation principle of the motor shown in FIGS. 5A to 5C elucidated by the present inventor will be described below, and its problems will also be mentioned.
FIG. 6 is a view for explaining the driving principle of the hetero-degeneracy longitudinal L1--bending B4 mode plate motor shown in FIGS. 5A to 5C.
As shown in column (A) in FIG. 6, this vibration driven motor produces a compound vibration of bending and longitudinal vibrations by applying high-frequency voltages A and B to the two electro-mechanical converting elements 2a and 2b, thereby generating elliptic motions at the distal ends of the driving force output portions 1a and 1b, i.e., generating a driving force.
Note that G indicates the ground. Assume that the two electro-mechanical converting elements 2a and 2b are polarized in polarities in the same directions, and the high-frequency voltages A and B have a time phase difference of .pi./2 therebetween.
Column (A) in FIG. 6 shows time changes in two-phase high-frequency voltages A and B input to the vibration driven motor at times t1 to t9. The abscissa of column (A) represents the effective value of the high-frequency voltage. Column (B) shows the deformation state in the section of the vibration driven motor, i.e., time changes (t2 to t9) in bending vibration generated in the vibration driven motor. Column (C) shows the deformation state in the section of the vibration driven motor, i.e., time changes (t1 to t9) in longitudinal vibration generated in the vibration driven motor. Column (D) shows time changes (t1 to t9) in elliptic motion generated in the projecting portions 1a and 1b of the vibration driven motor.
The operation of the vibration driven motor will be described below in units of time changes (t1 to t9).
At time t1, as shown in column (A), the high-frequency voltage A generates a positive voltage, and similarly, the high-frequency voltage B generates a positive voltage having the same magnitude as that generated by the voltage A. As shown in column (B), bending vibrations produced by the high-frequency voltages A and B cancel each other, and mass points Y1 and Z1 have zero amplitudes. As shown in column (C), the high-frequency voltages A and B produce longitudinal vibrations in a direction to expand. Mass points Y2 and Z2 exhibit a maximum expansion to have a node X as the center, as indicated by an arrow in column (C). As a result, as shown in column (D), the two different types of vibrations are combined, so that the synthesis of motions of the mass points Y1 and Y2 becomes a motion of a mass point Y, and the synthesis of motions of the mass points Z1 and Z2 becomes a motion of a mass point Z.
At time t2, as shown in column (A), the high-frequency voltage B becomes zero, and the high-frequency voltage A generates a positive voltage. As shown in column (B), the high-frequency voltage A produces a bending motion, so that the mass point Y1 oscillates in the positive direction, and the mass point Z1 oscillates in the negative direction. As shown in column (C), the high-frequency voltage A produces a longitudinal vibration, and the mass points Y2 and Z2 contract to be smaller than those at time t1. As a result, as shown in column (D), the two different vibrations are combined, and the mass points Y and Z move clockwise from the positions at time t1.
At time t3, as shown in column (A), the high-frequency voltage A generates a positive voltage, and similarly, the high-frequency voltage B generates a negative voltage having the same magnitude as that generated by the voltage A. As shown in column (B), bending motions produced by the high-frequency voltages A and B are synthesized and amplified. The mass point Y1 is amplified in the positive direction as compared to that at time t2, and exhibits a maximum positive amplitude value. The mass point Z1 is amplified in the negative direction as compared to that at time t2, and exhibits a maximum negative amplitude value. As shown in column (C), longitudinal vibrations produced by the high-frequency voltages A and B cancel each other, and the mass points Y2 and Z2 return to their initial positions. As a result, as shown in column (D), the two different types of vibrations are combined, and the mass points Y and Z move clockwise from the positions at time t2.
At time t4, as shown in column (A), the high-frequency voltage A becomes zero, and the high-frequency voltage B generates a negative voltage. As shown in column (B), the high-frequency voltage B produces a bending motion. The amplitude of the mass point Y1 becomes smaller than that at time t3, and the amplitude of the mass point Z1 becomes smaller than that at time t3. As shown in column (C), the high-frequency voltage B produces a longitudinal vibration, and the mass points Y2 and Z2 contract. As a result, as shown in column (D), the two vibrations are combined, and the mass points Y and Z move clockwise from the positions at time t3.
At time t5, as shown in column (A), the high-frequency voltage A generates a negative voltage, and similarly, the high-frequency voltage B generates a negative voltage having the same magnitude as that generated by the voltage A. As shown in column (B), bending motions produced by the high-frequency voltages A and B cancel each other, and the mass points Y1 and Z1 have zero amplitudes. As shown in column (C), the high-frequency voltages A and B produce longitudinal vibrations in a direction to contract. The mass points Y2 and Z2 exhibit a maximum contraction to have the node X as the center, as indicated by an arrow in column (C). As a result, as shown in column (D), the two different types of vibrations are combined, and the mass points Y and Z move clockwise from the positions at time t4.
As the time elapses from t6 to t9, bending and longitudinal vibrations are produced in the same manner as in the above-mentioned principle, and as a result, as shown in column (D), the mass points Y and Z move clockwise and make elliptic motions.
With the above-mentioned principle, the vibration driven motor obtains a driving force by producing elliptic motions at the distal ends of the driving force output portions 1a and 1b. Therefore, when the distal ends of the driving force output portions 1a and 1b are in press contact with an object 4, as shown in FIG. 7, the elastic member 1 moves relative to the object 4.
However, the motor shown in FIGS. 5A to 5C can realize a driving operation in only one direction since the producing direction of the elliptic motions is determined depending on the size of the elastic member 1 and the adhered positions of the electro-mechanical converting elements 2a and 2b.